Why do some rechargeable batteries work in MP3 players while others don't?

[AmberClad]

First of all, here're some details related to this little mystery:

NON-WORKING BATTERY
-------------------------------
Description: 1 x Panasonic Rechargeable AAA
Chemistry: NiCd
Rating: 220 mAh
Condition: Unknown (I was given these and don't know how many times they have been charged.)

WORKING BATTERY
-------------------------
Description: 1 x Duracell Dynacharge Rechargeable AAA
Chemistry: NiMH
Rating: 750 mAh
Condition: Brand New

The mAh rating is much higher for the Duracell because it's NiMH, that's normal AFAIK.

Now, the Panasonic AAA, if coupled with 3 other AAAs, will run a TI-83 just fine, so it's not caput. The MP3 player in question takes a single AAA and to turn it on, you press and hold the power button for ~2 sec. It refuses to turn on if the Panasonic battery is used.

So, any chemistry gurus or anyone else here care to shed some light on this little mystery?

 

[Bassyhead]

I'm not sure about NiMH, but the voltage on a NiCd battery is around 1.2 volts, not 1.5 like its alkaline counterparts. Moreover, a new alkaline battery usually has 1.6-1.8 volts when new. Perhaps the NiMH battery you've tried has a higher voltage at the terminals. I have a TI-83+ and in my experience it runs pretty well with low batteries for a long time. Perhaps, if you have a voltmeter or DMM, measure the terminals of the 2 batteries and see what you get.

 

[DrPizza]

Try this: take a dead battery and put it in with three good batteries in the TI83+

Most likely, it'll work just fine with a dead battery mixed in.

(in other words, I'll bet the Panasonic batteries are no good)

 

[MobiusPizza]

NiMH and NiCd generates completely different voltages
Perhaps different characteristic as well

Shouldn't mix them as it might damage

 

[Mark R]

The 'fully charged' voltage and 'nearly dead' voltage for NiCd and NiMH are very similar. When the battery runs out, the voltage just drops like a cliff.

Many gadgets will cut off when the battery voltage starts to dip so as to prevent deep discharge which is very hard on the batteries.

NiCd and NiMH batteries as they age, gradually lower their voltage - when brand new the voltage range can be 1.25 - 1.20 V, but after a lot of use (particularly overcharging) this can drop to as low as 1.1 - 1.0V. This gives the impression that the battery has lost capacity (it hasn't, the battery 'fuel gauge' is misinterpreting the voltage). Because you can temporarily improve the voltage with a deep discharge and full recharge, this gives the appearance of 'memory'. However, this is a feature of aging (usually premature due to bad charging) and is not readily reversible.

If your battery has aged to the point where it's voltage is below about 1.0V the chances are it won't be able to power the MP3 player on it's own. However, if mixed with 3 other good ones, the overall voltage (3 * 1.2 + 1.0V) may be above the cut off limit (probably 4 * 1.0 V)

Reminder: Always follow safety precautions - never mix batteries of different types, or in different states of charge. Always charge and connect correctly.

 

[AmberClad]

Thanks for the responses guys. I actually bought a set of 8 of these Duracells, so I won't have a problem powering my MP3 player, but I was still pretty curious about what might be wrong with the NiCd one. These look like some good insights.

btw - What would be the best way of completely discharging the bad batteries? I want to see if they're salvageable before I chuck them out.

 

[Mday]

The mAH rating is not "type" specific. When NiMH first came out, the prevailing NiCads had higher mAH ratings.

The reason the Panasonic with the 220 mAH rating, it does not provide sufficient power. now, 220mAH is extremely low, btw. It could mean that it's fairly old, and can no longer sustain itself, ie, its voltage would have fallen below operational levels for the player.

Also, do not mix battery types. I would further that with, do not mix "different" battery sets. Let's say next year, you get 8 more AAA NiMH batteries, keep those 8 apart from the 8 you already have.

 

[0roo0roo]

its just old. rechargables do die after X charges. i used to run a ti83 just fine with nicads

 

[onix]

I think your rechargables cannot deliver enough CURRENT (I), and hence enough POWER (P = I*V), at a their rated voltage (V), whereas NiMH can. A simple way to test is to buy a variable resistor (50 ohms to 5 kohm should be good enough) and hook it up to the battery. As you vary the resistance from high to low, use a digital voltmeter (DVM) to note when the voltage drops off. It will be different between your NiCd and NiMH. This feature to deliver current is different than the total ENERGY, i.e. mAH, that the battery stores.

Chances are that your MP3 player needs more current than some other electronics.

If you run this experiment, let us know the peak current you reached.